My almost 19 month old used to just be so sweet and easygoing. But recently she's been way more frustrated and gets very upset when she doesn't get her way. Your son may be dealing with teething or sibling rivalry, but he may also just be going through a new stage where he's got strong opinions. DD wanted to bring 3 things in the shower with us yesterday - a sippy cup of milk, a fabric based baby doll, and a piece of toast. I said no and I could tell she was getting really worked up. So I snuck the toast out of sight and let her bring the other 2 in. Little things like that make her really happy, but it's hard for her to communicate what she wants. I chalk it up to her starting to have strong (albeit random) opinions, and limited vocabulary to express it.

This exactly. My 20 mo does all of the same stuff: hitting, kicking, biting, ear piercing scream, etc. I think most of it is realizing that she has opinions on things. You ask her to pick up her toys, and she screeches at you and throws something. Or throws herself on the floor. She doesn't want to do it and that's how she's deciding to communicate it. But it got particularly bad after my itty bitty was born a few weeks ago. She was screeching at everything and throwing everything. I started putting her in her crib with her doll, paci, and blankets and letting her calm down every time she did it. It stopped it quickly.